1. Field of the Invention
The invention relates to a workpiece transfer apparatus and more specifically to transferring a workpiece processed at one processing facility to another processing facility on a production line provided with multiple processing facilities.
2. Description of the Related Art
An electronic circuit board transfer apparatus described in JP-H5-160597 provides an example of a workpiece transfer apparatus for transferring a workpiece processed at a processing facility to another processing facility.
The electronic circuit board transfer apparatus is provided with blocks D, C, B, and A in order from an upper stream of the direction for transferring electronic circuit boards. The block D carries in a board and prepares the board for the next process. The blocks C and B mount parts on the board. The block A carries out the board. The electronic circuit board transfer apparatus is also provided with a transfer mechanism having a belt conveyor. The electronic circuit board is placed on the belt conveyor and is transferred to the other blocks.
FIG. 8A shows an available workpiece transfer apparatus for transferring workpieces. The workpiece transfer apparatus includes rails 30a and 30b and workpiece graspers 10a and 10b hereafter also referred to simply as graspers. The rails 30a and 30b are provided above processing facilities 40a through 40d hereafter also referred to simply as facilities and extend in a direction for transferring a workpiece (not shown). The workpiece graspers 10a and 10b movably hang down from the rails 30a and 30b. The processing facilities 40a through 40d are provided with jigs 50a through 50d for mounting workpieces. For example, the workpiece transfer apparatus uses the workpiece grasper 10a to grasp a workpiece on the processing facility 40a. The workpiece transfer apparatus transfers a workpiece by moving the workpiece grasper 10a to a position above the processing facility 40b along the rail 30a and placing the workpiece on the processing facility 40b. The workpiece transfer apparatus thereby transfers workpieces from the facility 40a to the facility 40d. 
The rail 30a or 30b for hanging the grasper 10a or 10b has a certain length such as three to five meters for ease of manufacturing and installation. When the entire line is longer than the rail 30a or 30b, the rails 30a and 30b need to be connected to each other as shown in FIG. 8A. When the rails 30a and 30b are simply connected to each other, the grasper 10a moves only between the facilities 40a and 40b as shown in FIG. 8B. The grasper 10b moves only between the facilities 40c and 40d. No workpiece can be transferred between the facilities 40b and 40c. 
To address transfer between facilities, a feeder 400 may be provided between the facilities 40b and 40c, namely, at a position where a movable end of the grasper 10a is adjacent to that of the grasper 10b, as shown in FIG. 9. The feeder 400 has a slidable jig 500 for feeding workpieces.
The provision of the feeder requires an extra transfer operation of the feeder. In the present example, the number of transfer operation increases from three to four throughout the entire transfer path. Further, the provision of the feeder increases the cost of the transfer path and increases the cost of the entire production line.